With the progress of communication systems, consumers such as companies and individuals have used a wide variety of wireless terminals.
A current mobile communication system has affiliated with Third Generation Partnership Project (3GPP), for example, Long Term Evolution (LTE), LTE-Advanced (LTE-A), and the like. Such a mobile communication system requires a high-speed and high-capacity communication system capable of transmitting and receiving various types of data, such as image data, wireless data, and the like, beyond providing voice-oriented services.
For such a high-speed and high-capacity communication system, there is a need for developing technology capable of increasing the capacity of a user equipment by utilizing a small cell. Specifically, there is a need for developing technology which allows the user equipment to increase traffic throughput by transmitting/receiving data by using both of a macro cell having wide coverage and a small cell having relatively narrow coverage.
Also, the transmission speed and the consumed power of the user equipment are major factors to be considered when the user equipment transmits data to a base station. Accordingly, for the high-speed and high-capacity communication system, multiple cells are simultaneously used to increase the transmission speed of transmitted uplink data while the user equipment reduces power consumed for transmitting uplink data. To this end, there is a need for a specific procedure related to a method for transmitting/receiving uplink data and downlink data in a small cell environment.
Particularly, when the user equipment transmits a large amount of data at high speed by using multiple base stations, the user equipment needs to transmit, to the base station, the accurate amount of uplink data to be transmitted in uplink. Also, there is a need for a specific method for the user equipment to transmit uplink data to be transmitted.